Let's just be to the point and honest; you know you are not supposed to book an accessible room. You have already posted so yourself and read the info
DCL provides stating so. Please keep in mind there are very few accessible staterooms on any cruiseship. For many people the only option to cruise is when booking an accessible stateroom. Not available equals not going. These rooms are meant for those folks for instance using a wheelchair that simply can not enter a normal stateroom (doors are too cramped), let alone get into the bathroom. Those who can walk enough to not need a mobility aid in their room often book a regular room, having their aid stored either collapsed in the room or outside in a safe non blocking area. Most cruiselines, incl. DCL works with this trying to keep the few accessible rooms available to those with needs. Which includes providing all kinds of aids like a transfer bench for those that need to shower sitting down but can navigate a regular stateroom, hearing aids for those with hearing disabilities etc.
Unfortunately most cruiselines, DCL included, do not crack down enough on the "I need/ want more space therefor book an accessible stateroom" happening. A huge shame when somebody has no luxery of choice because of needing to use a mobility aid within the stateroom, being too big they can't fit through a regular door or shower, need the space in order to be able to use a lift to be able to go in and out of bed etc. etc.
Just having a tag is not a "qualifier" for such a room. A first time booker will be required to fill out a medical form. The form can be downloaded on the DCL website, amongst others. With the questions on their, they are trying to get clear if somebody actually needs the features in an accessible room or not. For instance questions about the type of mobility aid used etc. A physician will have to sign off on the fact that one needs an accessible stateroom and the stated needs and information are correct.
While I understand your situation, I think it's not the route to follow and try to book an accessible room without the absolute need for it. The stateroom being too cramped comes with one huge benefit; the ability to book a larger stateroom. Comes with a pricetag, totally understand that. But an option is better than none. If not already done; get some therapy and work on getting it manageble. The more you get to know your triggers, actions etc. the more knowledge you have to counter it. For instance, many will find an inside stateroom is a huge trigger as they have no direct way to look outside of the room. In those cases, an upgrade to a cat. 9 stateroom can make a huge difference. Having done many price outs, at the moment such a cat. is hardly really more expensive than an inside. I've ran into many differences of it being cheaper or perhaps $10,- more for a 9D then a 11C. Too many folks wanting to try those magical portholes.
Apart from DCL, I'ld grab the option of therapy with 2 hands if I were you. Cramped spaces are a fact in life that can't always be avoided. Finding ways to deal with the anxiety can have a huge positive benefit on quality of life. We all know cruising is the cherry on the cake, but a daily cake without cherry that tastes a lot better is great also.
If accessible rooms end up not all being needed for their features, they will be assigned to the general public. Won't happen until pretty last minute. Being upgraded is one of those factors that can result in this, having a GTY reservation also. So; that could be an other strategy to follow if you want to have a shot of having such a stateroom assigned if it's not needed. But as you can read from enough experiences; it's not uncommon for said rooms to be held back until even the day of check in. Which comes with another piece of knowledge; be at the port early if you want to see if any accessible stateroom is left available and you could switch to it.
As also posted; do your homework! Space isn't everything it's cracked up to be, unless one pays for it in a regular stateroom. Yes the accessible staterooms are larger, but that's because of a must. Resulting in stuff like furniture not being in these type of rooms that can be found in a non-accessible same cat. room. The occupancy number of these rooms tend to differ -again to make room to move around-, resulting in those fewer options that do have space for 4 being booked up first most of the times. Bathroom is "huge" for those viewing it through a not needing it situation. It's so for a reason again and will come with it's own guidebook. Floods for instance, that can or can not be managed. Less storage space is a common thing, for instance making place under the sink for someone to manouver their wheelchair and legs resulting in the storage underneath being removed. Electrical doors being installed that apparently already bug those who don't need the feature as it will take time before it closes -again to leave enough time for somebody needing it to safely go about- and thus waiting around to make sure the door is shut and nobody can get in without a key.